The present invention relates to a metal gasket having a main bead and an auxiliary bead to provide equal sealability around a hole to be sealed.
When a member having a hole therein is sealingly connected to another member having a hole, a gasket is installed between the two members to seal around the hole. Generally, the two members are connected together by a plurality of nuts and bolts passing through the members. In case the distance between the bolts is not so close, when the bolts are tightened, the equal surface pressure is not obtained around the hole. Namely, the sealability at areas adjacent the bolts is different from the sealability at areas away from the bolts.
For example, when a manifold gasket is securely installed between a manifold and a cylinder head by four bolts and nuts, the surface pressure of the manifold gasket around an exhaust hole is not even. Areas adjacent the bolts have high surface pressure, and as the distance from the bolts increases, the surface pressure decreases. As a result, the sealability at areas adjacent the bolts is superior to the sealability at areas away from the bolts.
Also, in a cylinder head gasket, if an oil hole or a water hole is provided at an end portion of a cylinder head gasket away from a tightening bolt, liquid may leak from the oil hole or water hole. This is because sealability around the hole is not even, so that if high pressure is suddenly applied, liquid may leak from the hole.
In order to seal around holes, such as cylinder bores, water holes and oil holes, it was proposed to form a bead on a steel plate to surround the hole. Even if a bead is formed around a hole, however, since a surface pressure on the bead is not even, liquid may still leak from the hole at a portion where the surface pressure of the gasket is not strong.
In this respect, it was proposed that a second bead is formed entirely around a first bead to prevent leakage by two beads. In case the two beads are provided, it is possible to apply strong tightening pressure to the gasket. However, the surface pressure applied onto the gasket or beads is not even. As a result, fluid may still leak at a portion of the gasket having lower surface pressure. Namely, even if two beads are formed around a hole, a low surface pressure portion is partly formed around a hole. Liquid may leak from a lower surface pressure portion of a gasket.
Accordingly, one object of the present invention is to provide a metal gasket, which can provide equal sealability around a hole, when tightened.
Another object of the invention is to provide a metal gasket as stated above, which can securely prevent leakage of fluid around fluid holes of the gasket.
A further object of the invention is to provide a metal gasket as stated above, which can be manufactured easily and economically.
Further objects and advantages of the invention will be apparent from the following description of the invention.